Memory is crucial to identity and survival, and the hippocampus is required for normal memory. The causal relationship between hippocampal cell activity and learning and memory performance, however, remains unknown because few experiments record neuronal firing while memory demands are varied and other aspects of behavior are held constant. Aim 1. To identify learning-dependent changes in neuronal encoding by recording groups of hippocampal neurons while rats perform a task that requires the hippocampus. Successful newlearning that requires the hippocampus should require the formation of new and persistent firing patterns by hippocampal neurons. Rats will be trained in a + maze task that can be solved by either hippocampus-dependent or independent strategies. Groups of hippocampal cells will be recorded in rats that behave identically but differ in learning ability, memory strategy, and hippocampal function. Probes will test the strategies used by each rat, and unit activity will be compared in normal place and response learners, and rats with fornix or caudate lesions. Aim 2. To test the generality of the results in Aim 1, neuronal activity will be recorded in rats trained in a distinct type of learning, the social transmission of food preference. A subset of dynamic neuronal responses may be required for all types of hippocampus-dependent learning, independent of behavioral expression, type of motivation, and specific content of learning. Hippocampal neurons in normal rats should develop persistent olfactory associations between the arbitrarily selected novel food odors and the odor of carbon disulfide, the signal of food safety. Aim 3. To test if temporal relationships among spike trains encode memory by comparing real-time ensemble activity in the hippocampus. Significant memory information may be encoded by the temporal relationships among neurons action potentials. The temporal dynamics of spiking within ensembles recorded during identical behaviors but different memoryloads will be assessed using published and a new method. The analysis will begin by comparing spike records as rats traverse the start arm of a + maze during right and left turns.